Absorbent articles for absorbing body fluids are well known. These articles typically comprise an absorbent core covered by a topsheet, which is positioned adjacent to, and, in use, may contact the user's skin. The topsheet for use in an absorbent article is typically an apertured film, nonwoven, or laminated combinations thereof. Examples of such absorbent articles include diapers, incontinent articles, and sanitary napkins.
One problem associated with absorbent articles is maintaining the dryness of the wearer-facing surface of the topsheet. Generally, when the wearer-facing surface is kept dry, the absorbent article is more comfortable. To maintain a dry wearer-facing surface, the absorbent article should be able to eliminate both dynamically-deposited and statically-retained fluids from the topsheet. Dynamically-deposited fluids are generally voluminous fluids expelled by the user, while statically-retained fluids are residual fluids held in or on the topsheet by surface tension. Each presents different problems. On one hand, dynamically-deposited fluids must be rapidly transmitted to the absorbent core to minimize wearer discomfort and to prevent the lateral runoff of fluids leading to leakage and garment soiling. This rapid transmission of dynamically-deposited fluids by the topsheet to the absorbent core is at a rate greater than the absorbent rate of the core. This causes pooling of unabsorbed fluid on the core surface and leads to higher levels of statically-retained fluid over a larger area of the topsheet. Regardless of the cause, the presence of these statically-retained fluids results in a highly uncomfortable and undesirable sensation.
Eliminating these two types of fluids from the topsheet typically requires two different, and often competing, mechanisms. For example, to remove statically-retained fluid from the surface of an absorbent article, one approach has been to interpose an additional layer, such as a nonwoven, between a nonwoven topsheet and an absorbent core. The interposed nonwoven layer typically has a pore size distribution whose average pore size is smaller than the average pore size of the topsheet. This allows the interposed nonwoven layer to transmit static fluid from the topsheet toward the absorbent core by capillary action. Although this may be effective for removing statically-retained fluids, the smaller average pore size in the interposed nonwoven layer interferes with the rapid transmission of dynamically-deposited fluids to the underlying absorbent core. While this has some benefit as it slows transmission to the core and can prevent fluid from accumulating on the core surface, this leads to fluid accumulating in the interposed nonwoven layer and can lead to fluid accumulation on or in the topsheet or even to leakage from the edges of the absorbent article. Additionally, if the absorbent core becomes saturated, the interposed nonwoven layer can wick moisture in the reverse direction toward the topsheet especially when the article is being compressed.
To handle dynamically-deposited fluids, one approach involves interposing a perforated thermoplastic film such as described in U.S. Pat. No. 6,700,036 between a nonwoven topsheet and an absorbent core of an absorbent article. The film rapidly transmits dynamically-deposited fluid from the topsheet and tends to disperse the fluids to the core area beyond the primary insult zone. This approach, however, is faced with a number of drawbacks stemming from the film's segregation of the topsheet and core. For example, any fluid that does not penetrate the film to be absorbed in the core may be wicked up by the topsheet to the wearer-facing surface. Furthermore, the film traps moisture in the nonwoven topsheet since it blocks the core from wicking moisture away from the topsheet by interrupting the capillary gradient. Although films with capillary-sized apertures are known for use as topsheets, see, for example, U.S. Pat. No. 4,637,819, their effectiveness in removing residual fluid from a nonwoven topsheet is questionable since they would seemingly lack sufficient contact with the topsheet. These apertured films further suffer from their inability to rapidly transmit the dynamically-deposited fluid to the core and to provide sufficient core-side volume space to disperse the fluid to areas of unsaturated core.
Other approaches for eliminating statically-retained fluid include using an apertured formed film as a topsheet. A problem with this approach is that there is a considerable upper surface area which does not allow passage of fluid through the film to an absorbent core below. This upper surface can remain wet, particularly if this surface is hydrophilic. This wetness can cause the film to adhere to the wearer's skin when brought into contact during use. Another problem with this approach is that some consumers do not like the plastic feel associated with formed films.
Therefore, there is a need for an absorbent article that can transmit both dynamically-deposited fluids and statically-retained fluids. The present invention fulfills these needs among others.